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Diaphragm Analysis (Load Linking)

Structural engineers sizing shear walls and lateral force-resisting systems in wood-framed buildings. Link shear demand directly from the diaphragm into connected shear wall calculators so the full lateral load path updates automatically when geometry or loads change.

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What it calculates

Wall-line shear demands link directly to connected shear wall calculators so lateral load distribution updates automatically. Analyse flexible diaphragms with unlimited braced wall lines and lateral loads using FEA. Wind and seismic demands are distributed to each wall line for direct use in shear wall design.

How it calculates

The Diaphragm Analysis calculator models a flexible floor or roof diaphragm as a 1D deep beam spanning between braced wall lines, using FEA to distribute applied lateral forces.

Structural model

The diaphragm is modelled using a stiffness-matrix FEA solver. Wall lines are treated as support locations at the positions you specify. Lateral loads are applied in the plane of the diaphragm. The model assumes flexible diaphragm behaviour - load is distributed to wall lines by tributary width, not by wall stiffness. Diaphragm torsion (rigid diaphragm redistributions) is not modelled.

Load types and combinations

Wind (W) and seismic (E) are treated as independent load types. Distributed loads are entered over a tributary height (the story height contributing to the diaphragm level) and converted to in-plane line loads. Concentrated seismic forces can also be applied directly as point loads at specific positions, useful when level-by-level seismic forces from the equivalent lateral force procedure are being distributed.

The display load case can be set to Wind or Seismic to inspect each independently, with the calculator identifying the governing case for the maximum shear demand.

Shear demand

The governing in-plane shear force anywhere along the diaphragm span is the maximum shear under the governing load case. The governing load type (Wind or Seismic) is reported alongside the demand.

Wall-line demands table

For each braced wall line the calculator outputs:

  • Wind load in wall line R_w: total force the wall must resist under wind
  • Seismic load in wall line R_e: total force the wall must resist under seismic

These are derived from the support reactions in the FEA model - the force required at each wall position to maintain equilibrium under the applied lateral loads.

Load linking outputs

All wall-line reactions are available as named linkable outputs. In a Calcs.com project, each wall-line reaction can be connected directly to the corresponding shear wall calculator. When you update the diaphragm span, story height, or lateral forces, all connected shear wall calculators receive updated demand values without manual data transfer.

Related calculators

Beam Analysis→Truss Analysis Wizard→Portal Frame Analysis Wizard→Seismic Analysis (ASCE 7-16)→

Frequently asked questions

What analysis method does this calculator use?
The calculator performs load distribution analysis on flexible diaphragms using a FEA-based beam model. It treats the diaphragm as a simple deep beam spanning between braced wall lines. Only simple diaphragms without torsion are modelled; the diaphragm is assumed flexible. Sheathing and nailing pattern capacity are not checked - the output is load demand for downstream wall design.
What inputs does the calculator require?
You enter the diaphragm length and the positions of braced wall lines, then apply lateral loads as distributed loads (wind pressure on the building face, applied over tributary height) or as concentrated and line loads (seismic forces from above floors). Wind (W) and seismic (E) are each entered as separate load types.
What outputs does the calculator produce?
The calculator outputs the governing shear demand in the diaphragm (V), the governing load type for shear, and a demands table showing the total wind and seismic load transferred into each braced wall line. These wall-line reactions are available for direct load linking to shear wall calculators.
Can it model diaphragms with more than two shear walls?
Yes. You can define unlimited braced wall lines at any position along the diaphragm span. The FEA model distributes loads to all wall lines according to tributary width, and the demands table shows the reaction at every line.
Does the calculator check the diaphragm sheathing capacity?
No. The calculator is for load distribution analysis only - it determines the shear demand that the diaphragm and its chord members must resist, and the force each shear wall line must be designed for. Sheathing selection, nailing patterns, and chord design are performed separately.
How does load linking work with shear wall calculators?
Wall-line reactions from the demands table are exported as linkable outputs. In a Calcs.com project you connect them to the shear wall calculators for each braced wall line. When you adjust the diaphragm geometry, tributary height, or lateral loads, the shear wall demand updates automatically through the link.

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